Vision control panels are well known, for example panels according to GB 2 165 292 or EP 0 880 439. Panels according to GB 2 165 292 typically comprise a transparent material which is partially imaged with an opaque “silhouette pattern” onto which is superimposed a design, such that the design is visible from one side of the panel but is not visible from the other side. They may also have a second design that is visible from the other side but not visible from the first side. Panels according to EP 0 880 439 typically comprise a transparent material that is partially imaged with a translucent “base pattern” typically comprising a white base layer onto which is superimposed a translucent design, which is visible from the first side and a mirror image of the design is visible from the other side when there is sufficient illumination on one or both sides. The design visible from one side can be illuminated from the opposite side. There are many other types of panel disclosed in these two patents which may collectively be termed vision control panels.
GB 2 165 292 and GB 2 188 873 disclose methods of printing superimposed layers of ink with exact registration by applying layers of ink of greater area than required in the finished product and removing unwanted ink to leave the desired remaining layers of ink in exact registration.
EP 0 858 399 and U.S. Pat. No. 6,506,475 (WO 02/070269) disclose methods of managing the inevitable lack of registration of normal printing methods in order to manufacture vision control panels with the desired perceived colours, which would not otherwise be consistently achieved.
EP 0 904 206 discloses manipulation by a computer of a design to create unprinted areas of a transparent material to which the design is applied. It also discloses the digital inkjet printing of vision control panels including the use of both water-based and solvent-based ink; it also identifies problems of opacity and the problem of registration of multiple layers associated with inkjet printing. It discloses certain methods of seeking to overcome these problems but it does not disclose the use of UV curable inkjet inks or UV inkjet printing machines.
EP 0 934 169 and WO 04/0045937 disclose methods of making vision control panels by digital inkjet printing of a pre-printed “print pattern”, typically a screen printed pattern of white-on-black dots or lines. Together, these documents disclose possible inkjet printing of the design layer by water-soluble ink or solvent ink or UV curable ink but these methods are based on the premise that inkjet printing of all layers is impractical.
In making one-way vision panels according to GB 2 165 292, it is typically required to have a black layer of the silhouette pattern visible from the other side to the design, in order to provide the best possible through vision. However, a white layer is typically required as a background to printing the design colours and more than one layer of white is typically required in order to create a suitable white background for printing the design. The use of a silver layer intermediate a white and black layer to achieve a more visually opaque white (higher thickness and/or saturation) is well known and specifically disclosed in the making of vision control panels in BP 0 858 399 and WO 02/070269.
EP 1 535 750 A2 discloses the computer manipulation of artwork by means of a computer “window wizard” to produce see-through graphic panels. WO 2005/053963 and image manipulation software manuals, such as for Adobe Photoshop™, disclose the cropping of an image around subject matter in a graphic image and providing a mask background, typically white, to the cropped image. WO 2005/053963 also discloses UV inkjet printing onto transparent substrates.
So-called “selective blocking” of areas of see-through graphic panels has been practised since the 1980's by licensees of Contra Vision Ltd, UK, for example to highlight subject matter or to enable small print to be visible, by infilling portions of the panel that would otherwise be transparent in a uniform pattern, for example, of dots or lines.
Digital UV inkjet printers with multi-colour process inks, for example cyan, magenta, yellow and black (CMYK), and additional white or other “spot colours” are known. The use of continual mechanical stirring or other method of ink agitation such as inert gas-burst and temperature control to assist the digital printing of white ink are known.